1. Field of the Invention
This invention relates to a vibrating input pen for coordinate input of a coordinate input apparatus, and more particularly, to a coordinate input apparatus in which vibration input from the vibrating input pen is detected by a plurality of sensors provided on a vibration transmitting plate, and thereby determining the coordinates of the vibrating input pen on the vibration transmitting plate.
2. Description of the Related Art
Among various kinds of coordinate input apparatus which have been proposed, there is an apparatus utilizing the transmission of vibration as a method using a simple yet high reliability structure. This apparatus detects vibration input from a vibrating input pen with a plurality of sensors provided on a vibration transmitting plate, and thereby detects the coordinates of a position of the vibrating input pen on the vibration transmitting plate.
The vibrator used in the above-described vibrating input pen is an electromechanical transducer having the direction of its polarization perpendicular to the direction of its vibration (this kind of element will be hereinafter termed a "direction-K31 piezoelectric element"). FIGS. 7(A) and 7(C) are cross-sectional views of principal parts showing the internal structures of vibrating input pens which have been used: FIG. 7(A) illustrates a configuration using a cylindrical piezoelectric element; and FIG. 7(C) illustrates a configuration using a columnar piezoelectric element.
In FIGS. 7(A) and 7(C), a horn unit 52 transmits vibration from a vibrator 41 or 42 to a vibration transmitting plate. A pen case 31 receiving components of the vibrating input pen is shaped to be easily held by a hand. In FIG. 7(A), the vibrator 41, which is a cylindrical piezoelectric element, is a direction-K31 piezoelectric element. Hence, the vibrator 41 is configured so that electric energy is supplied from electrode springs 361 and 371, serving as driving electrodes for the vibrator 41, which are in pressure contact with the inner and outer surfaces of the cylinder, respectively. Since vibration is generated in the direction of the axis of the pen as shown in FIG. 7(B), the transmission efficiency of vibration to the horn unit 52 is high. In case of FIG. 7(C), the vibrator 42 (FIG. 7(D)), which is a columnar piezoelectric element, is configured so that electric energy is supplied from soldered lead wires L360. In this case, since the vibrator 42 is a direction-K31 piezoelectric element, the direction of its vibration is perpendicular to the direction of the axis of the pen. Accordingly, in order to prevent the transmission efficiency of vibration to the horn unit 52 from being substantially decreased, the vibrator 42 and the horn unit 52 are fixed together by a means, such as bonding or the like.
However, when the direction-K31 piezoelectric element is cylindrical as shown in FIG. 7(A), even if the pen point and the axis of the cylindrical piezoelectric element in the direction of vibration are aligned on a line, pressures by the electrodes provided on the inner and outer surfaces of the piezoelectric element cannot be uniform. Hence, physical vibration characteristics change due to factors such as maldistribution of piezoelectric characteristics caused by an unbalance in external forces on the element when the electrodes are mounted, and the vibration of the vibrating input pen has directivity relative to the axis in a vibration mode. As a result, a stable coordinate detection operation has sometimes been impossible.
On the other hand, when the direction-K31 piezoelectric element is columnar as shown in FIG. 7(C), since the element vibrates in a direction perpendicular to the axis of the pen, the element must be fixed to the pen point (the horn unit 52) by an adhesive or the like in order to increase the transmission efficiency of vibration. In this case, it is impossible to replace only the pen point when the pen point is used up or in an unexpected accident, such as breakage of the pen point or the like. As a result, the user must bear a high cost burden.
Furthermore, in the case of the cylindrical direction-K31 piezoelectric element, if bonding is used in order to increase the transmission efficiency of vibration and also to supply electric power to the element, the resonance characteristics of the vibrating input pen must be uniform in order to maintain accuracy in the coordinate input apparatus. As a result, the vibrating input pen using such an element has the disadvantages that productivity in the production of the pen is decreased due to factors such as control of the thickness of an adhesive layer for bonding, and the above-described directivity appears when, for example, bubbles are formed in the adhesive layer, or partially imperfect bonding is performed, causing a decrease in the production yield.